Refrigerant System with Pulse Width Modulated Components and Variable Speed Compressor

ABSTRACT

A variable speed drive is provided for operating a compressor motor in a refrigerant system. When a low load situation has been determined by the refrigerant system controls, the variable speed drive operates the compressor motor at lower speed mode of operation. Further, the operation of the variable speed drive is combined with a pulse width modulation control of different system components. In particular, at least one valve or compressor can be can be rapidly cycled by the control to regulate amount of refrigerant passing through the valve or compressor. Example valves would include a shut-off valve for an economizer cycle, an unloader valve, or a suction modulation valve.

BACKGROUND OF THE INVENTION

This application relates to a control for a refrigerant system having avariable speed compressor, and wherein pulse width modulationtechnologies are utilized to provide further control over the system.

Refrigerant systems are utilized in many applications to condition anenvironment. In particular, air conditioners and heat pumps are employedto cool and/or heat air entering the environment. The cooling or heatingload of the environment may vary with ambient conditions, occupancylevel, other changes in sensible and latent load demands, and as thetemperature and/or humidity set points are adjusted by an occupant ofthe environment.

A feature that is known for improving the efficiency of refrigerantsystems is the use of a variable speed drive for the compressor motor.Often, the compressor need not be operated at full speed, such as whenthe cooling load on the refrigerant system is relatively low. Under suchcircumstances, it might be desirable to reduce the compressor speed, andthus reduce the overall energy consumption of the refrigerant system.Implementation of a variable speed drive is one of the most efficienttechniques to enhance system performance and reduce life-cycle cost ofthe equipment over a wide spectrum of operating environments andpotential applications, especially at part-load conditions.

However, compelling reliability concerns set a lower limit to thedesirable compressor speed reduction. As an example, inadequatelubrication of the compressor elements may present a problem at lowoperating speeds. Further, certain types of compressors require aminimum operating speed to provide radial compliance. As an example, ascroll compressor could have a dramatic loss in performance due to aloss of radial compliance should it operate below a minimum speed.

Various other features are known for providing variations in systemcapacity in a manner other than lowering the speed of the compressor. Asan example, economizer cycles are known as are unloader cycles. However,even with the provision of these cycles in a system having a variablespeed drive for its compressor, it would be desirable to provide evenmore variability in the system capacity.

Another approach which has been utilized in the prior art to change thecapacity of a refrigerant system is the use of pulse width modulation tocontrol valves such as a shut-off valve on an economizer cycle, and/or ashut-off valve on an unloader line, and/or a shut off valve on asuction. By rapidly cycling these valves utilizing pulse widthmodulation techniques, additional capacity control is provided. Thepulse width modulation of the internal scroll elements can also beapplied in conjunction with variable speed drive operation. In thiscase, as known in the art, the scroll elements are separated from eachother in a pulse width manner to control the amount of refrigerantpumped by the compressor. These pulse width modulation techniques forcontrol of a valve or internal scroll compression elements have not beenutilized, however, in refrigerant systems having a variable speed drivecompressor.

SUMMARY OF THE INVENTION

In the disclosed embodiment of this invention, a compressor is providedwith a variable speed drive. When a need for a low capacity is detected,the compressor is moved to a low speed to maintain adequate conditionsin the environment without switching to a start-stop mode of operation.The compressor is incorporated into a refrigerant system, which has apulse width modulation control for cycling some component in the system,other than cycling on and off the compressor motor. In disclosedembodiments, the cycled component is a valve, and may be a suctionvalve, and/or an economizer cycle shut-off valve and/or an unloadervalve and/or cycled component is one of the scroll compressor pumpingelements. By cycling these components on and off, the amount ofrefrigerant delivered to various locations in the refrigerant cycle islowered, and thus the capacity can be lowered without lowering thecompressor motor speed beyond the safe regime.

Although, for illustrative purposes, the operation of the valves in thisinvention is described in relation to refrigerant systems incorporatingscroll compressors, it could be applicable to any variable speedcompressor.

These and other features of the present invention can be best understoodfrom the following specification and drawings, the following of which isa brief description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic view of a refrigerant system incorporating thepresent invention.

FIG. 1B shows an alternative embodiment.

FIG. 2 shows another schematic of a refrigerant system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A refrigerant system 19 is illustrated in FIG. 1 having a scrollcompressor 21 incorporating a non-orbiting scroll member 22 and anorbiting scroll member 24. As is known, shaft 26 is driven by anelectric motor 28 to cause the orbiting scroll member 24 to orbit. Asshown, a variable speed drive 30 is schematically connected to drive theelectric motor 28. An oil sump 32 and an oil passage 34 in the shaft 26supply oil to the various moving elements in the compressor 21, asknown.

A condenser 36 is positioned downstream of the compressor 21, anexpansion device 38 is located downstream of the condenser 36, and anevaporator 40 is positioned downstream of the expansion device 38, asknown. As is also known, the compressor 21 is driven by the electricmotor 28 to compress the refrigerant vapor and to drive it through therefrigerant system 19. Oil from the oil sump 32 is delivered to thecompressor elements to provide proper lubrication of the compressorcomponents such as the crankcase bearing 100, orbiting scroll bearing102, the non-orbiting scroll 22 and the orbiting scroll 24, while someamount of oil leaves the compressor 21 with the refrigerant and iscirculated through the refrigerant system 19. One of the most typicaloil delivery systems of a scroll compressor is also shown in FIG. 1,where the oil from the oil sump 32 is picked up by the oil pick up tube110, and delivered along the oil passage 34 to various compressorcomponents as described above. Some of the oil can also be deliveredthrough the suction port 120 by a refrigerant entering the compressor.However most of the oil delivery is accomplished by delivering the oilfrom the oil sump as described above. In the prior art, when a variablespeed drive has been implemented in a refrigerant system, the designerhas been limited by a minimum operational speed of the shaft 26 for thecompressor 21. If the speed dropped below a certain level for extendedperiod of time, an insufficient amount of oil would be delivered throughthe oil passage into the compressor components that need to belubricated. Thus, for a low cooling load situation, where only a smallamount of the compressed refrigerant mass flow is needed to becirculated through the system, a minimum speed requirement (for example45 Hz) is often a limiting factor in ensuring that adequate amount ofoil is provided to the compressor components. Further, the operationabove a minimum speed would also ensure that the radial compliancenecessary for efficient operation of the scroll compressor is not lostdue to unduly low motor speed. As known, it is important to match thedelivered capacity to the system load. Since the compressor operatingspeed often cannot be reduced below a certain threshold for capacityshedding, additional efficient means are required to reduce the capacitydelivered by the unit without cycling the unit on and off for tighttemperature control within the cooled environment. The description belowprovides additional means of efficiently shedding the capacity bycoupling the compressor variable speed operation with pulse widthmodulation of different system components.

FIG. 1 shows additional features that may be incorporated into therefrigerant system 19. As an example, an economizer cycle is includedand has an economizer heat exchanger 18. A main liquid line 13 has a tapline 11 tapped off of the main liquid line and passed through aneconomizer expansion device 115. The tap line 11 and the main liquidline 13 both pass through the economizer heat exchanger 18. In fact, andin practice, the refrigerant flow in the tap line is typically in thecounterflow direction through the economizer heat exchanger in relationto the flow in the main liquid line 13. However, to simplify theillustration in this figure, they are shown in the same direction. As isknown, the economizer circuit subcools the refrigerant in the mainliquid line, and thus enhances performance (capacity and/or efficiency)of the refrigerant system 19. An economizer injection line 20 is shownextending back to the compressor 21, and injects an intermediatepressure refrigerant into compression chambers through passages such aspassage 23. The function and structure of the economizer circuit isknown, however, its inclusion with the inventive motor control 30provides a refrigerant system that has even greater flexibility toenhance operation of the refrigerant system 19.

An optional unloader line 17 includes an unloader valve 200. Theunloader valve 200 is selectively opened to return partially compressedrefrigerant from the compression chambers through the passages 23 backto a suction port 120 of the compressor 21. The unloader functionpresents a refrigerant system designer with an extra degree of freedomfor performance adjustment and optimization. The unloader valve can belocated inside or outside of the compressor, as known.

Essentially, when a greater system capacity is desired, the economizerfunction may be utilized with the unloader valve shut. Alternatively, ifa lower capacity is necessary, the economizer expansion device 115 (or aseparate shut-off device) is shut, with the unloader valve 200 opened.In this manner, the amount of compressed refrigerant delivered to thecondenser 36 is reduced. Also, if desired to provide anotherintermediate stage of capacity for the refrigerant system 19, theeconomizer function can be combined with the unloader function byopening both the economizer expansion device 115 and the unloader valve200. Shutting the flow in the economizer injection line and closing theunloader valve 200 also achieve another alternate intermediate stage ofcapacity unloading.

These system configurations in combination with the variable speed motorcontrol disclosed below provides even greater freedom and flexibility toa refrigerant system designer for controlling the delivered systemcapacity

In this case, the control 30 may incorporate more than a variable speeddrive, but may also be a microprocessor or other type control that iscapable of providing pulse width modulation control to the economizervalve 115 (which in this case would be a shut-off valve), and/or theunloader valve 200, and/or a suction modulation valve 210.

Also as known in the art, the pulse width modulation can also be used topulse width modulate the scroll compression elements itself, in thiscase the scroll elements would be separated from each other in a pulsewidth manner to control the amount of the refrigerant pumped by thecompressor.

FIG. 1B shows an embodiment 301, schematically. It is known that theorbiting scroll member 302 and the non-orbiting scroll member 304 may bebiased together by a gas in a chamber 306. Opening and closing the valve310 can control pressure in chamber 306. As shown, the valve 312communicates via line 308 with another pressure source that is atdifferent pressure than pressure in the chamber 306 when the valve 310is closed. When the pressure in the chamber 306 is reduced below acertain level the scroll members will separate from each and the amountof refrigerant pumped by the compressor is then reduced. When thepressure in the chamber 306 is increased above certain level the scrollswill come into contact with each other and then the normal compressionprocess will resume. The valve can be controlled by a pulse widthmodulation control 312. Thus, by modulating the pressure in the chamber306, the two scroll members 302 and 304 can be allowed to periodicallymove away from, and come into contact with, each other. It should benoted that the schematic shown in FIG. 1B is presented for anillustration purpose only. For example, instead of allowing the scroll304 to move axially in and out of contact with the scroll 302, thescroll 302 can be allowed to move axially while the scroll 304 remainsessentially stationary in the axial direction. The valve 312 can belocated internal or external to the compressor.

While the schematic shows the control providing pulse width modulationcontrol to each of these valves and/or compressor elements, in otherembodiments any combination of the three vales and/or compressor, oreven other valves can be utilized. By rapidly cycling these valves toopen and closed position (closing can be partial or complete), theamount of refrigerant passing through any one of the valves andcompressor can be varied to vary capacity. As an example, once thecompressor speed has been lowered, and additional capacity reduction isdesired, a valve or compressor can be cycled to further reduce thesystem capacity. It should be noted that normally the compressor speedreduction would be applied first to shed the capacity, since this is themost efficient means to do so than other methods of unloading.

The present invention provides efficient means to efficiently andprecisely control capacity of the refrigerant system 19 by employingvarying methods of pulse width modulation of various system componentscoupled with the use of a variable speed drive motor. The motor drivecan be varied in speed when there is a need for capacity adjustment. Theeconomizer circuit can also be turned on or off to vary capacity. Theunloader function can also be utilized. In addition, and in combinationwith each of the above options for this control, the present inventionalso allows the control to modulate the flow of refrigerant through anyone of valves 115, 200 and 210 and/or through modulation of thecompressor pumping elements itself. In this manner, the capacity can befurther reduced without unduly lowering the speed of the compressormotor 28 beyond its safe threshold of operation.

FIG. 2 shows another embodiment 300 wherein the valves 200 and 210 areinternal of the compressor shell as are the flow passages. It should benoted that while in FIG. 2 the valves are all shown as located insidethe compressor, a compressor designer may choose to locate some of theminternally and some of them externally. In addition, the shut-off valve220 for the economizer line is shown to be separate from the expansionvalve. If the valve 220 is located externally, its function can becombined with the use of an expansion valve. Also while valves are shownas separate components, its function can be combined into a singlethree-way valve as known in the art. Each or some of the valves 220, 200and 210 can be controlled by pulse width modulation techniques.

It should be understood that the motor control 30 includes a programthat takes in inputs from various locations within the refrigerantsystem, and determines when a lower speed for the compressor motor wouldbe desirable and when the pulse width modulation of the pulse widthmodulated components needs to be initiated. The controller can alsodecide when the system needs to be operated in economized,non-economized, and by-pass unloading modes or any of its combinationsas described above. Controls capable of performing this invention withsuch valves and compressors are known.

A worker of ordinary skill in the art would recognize when a lower speedmight be desirable and preferred in comparison or in addition to otheravailable options.

It should be understood that although this invention is described inrelation to refrigerant systems incorporating scroll compressors, itcould be applicable to any variable speed compressor, including scrollcompressors, screw compressors, reciprocating compressors, rotarycompressors, etc. The application of this technique can for example, beapplied to refrigeration systems used in transportation container units,truck/trailer application, supermarket refrigeration application, aswell as cooling or heating industrial buildings and residential housesas well as used for water heating applications. Although a preferredembodiment of this invention has been disclosed, a worker of ordinaryskill in this art would recognize that certain modifications would comewithin the scope of this invention. For that reason, the followingclaims should be studied to determine the true scope and content of thisinvention.

1. A refrigerant system comprising: a compressor and an electric motorfor driving said compressor, a variable speed drive for varying a speedof operation of said electric motor; a condenser downstream of saidcompressor, an expansion device downstream of said condenser, and anevaporator downstream of said expansion device; said variable speeddrive moving said motor to low speed operation, and said variable speeddrive operating said motor at a low level of speed; and a pulse widthmodulation control for controlling at least one system component.
 2. Therefrigerant system as set forth in claim 1, wherein said pulse widthmodulation control controls at least one valve.
 3. The refrigerantsystem as set forth in claim 2, wherein an economizer circuit isincorporated into the refrigerant system.
 4. The refrigerant system asset forth in claim 3, wherein the said at least one system component isa shut-off valve associated with said economizer circuit.
 5. Therefrigerant system as set forth in claim 2, wherein said compressor isprovided with an unloader circuit.
 6. The refrigerant system as setforth in claim 5, wherein said at least one system component is a valveassociated with said unloader circuit.
 7. The refrigerant system as setforth in claim 2, wherein the refrigerant system is provided with bothan economizer circuit and an unloader circuit.
 8. The refrigerant systemas set forth in claim 7, wherein said at least one system componentincludes a valve associated with said economizer circuit and a valveassociated with said unloader circuit.
 9. The refrigerant system as setforth in claim 2, wherein said at least one system component is a valvefor controlling the mass flow of refrigerant delivered to saidcompressor from said evaporator.
 10. The refrigerant system as set forthin claim 1, wherein said at least one system component is external to ashell for said compressor.
 11. The refrigerant system as set forth inclaim 1, wherein said at least one system component is internal to ashell for said compressor.
 12. The refrigerant system as set forth inclaim 1, wherein said compressor is selected from the group consistingof a scroll compressor, a rotary compressor, a reciprocating compressor,and a screw compressor.
 13. The refrigerant system as set forth in claim1, wherein said at least one component is a pulse width modulatedcontrol to hold the orbiting and non-orbiting scroll member in a scrollcompressor together or allow them to move away from each other.
 14. Therefrigerant system as set forth in claim 1, wherein said system isselected from the group consisting of a container refrigeration system,a truck/trailer system, a supermarket refrigeration system, aresidential air conditioning system, a residential heat pump system, acommercial air conditioning system, a commercial heat pump system, and awater heating system.
 15. A method of operating a refrigerant systemcomprising the steps of: (1) providing a compressor with a variablespeed drive, and monitoring a load on a refrigerant system associatedwith said compressor; (2) identifying a low load situation, and movingsaid compressor to a low speed operation when a low load situation hasbeen identified; and (3) providing pulse width modulation control for asystem component to allow the variation of capacity from the refrigerantsystem by both varying the speed of the compressor, and varying theoperation of said other component.
 16. The method as set forth in claim15, wherein said pulse width modulation control controls at least onevalve.
 17. The method as set forth in claim 16, wherein an economizercircuit is incorporated into the refrigerant system, and said at leastone system component a shut-off valve associated with said economizercircuit.
 18. The method as set forth in claim 16, wherein saidcompressor is provided with an unloader circuit, and said at least onesystem component at is a valve associated with said unloader circuit.19. The method as set forth in claim 16, wherein the refrigerant systemis provided with both an economizer circuit and an unloader circuit, andsaid at least one system component includes a valve associated with saideconomizer circuit and a valve associated with said unloader circuit.20. The method as set forth in claim 15, wherein said at least onecomponent is external to a shell for said compressor.
 21. The method asset forth in claim 15, wherein said at least one component is internalto a shell for said compressor.
 22. The method as set forth in claim 15,wherein said other component is a valve for controlling the amount ofrefrigerant delivered to said compressor from said evaporator.
 23. Themethod as set forth in claim 15, wherein said at least one component isa pulse width modulated control to hold the orbiting and non-orbitingscroll member in a scroll compressor together or allow them to move awayfrom each other.